EFFECTS OF MAGNETIC RESONANCE ON TEMPERATURE AND ADHESION EFFICACY OF ORTHODONTIC DEVICES

Magnetic resonance (MRI) is a widely used diagnostic technique. Often, patients wearing orthodontic appliances are requested to remove appliance even when the MRI exam involves anatomic areas far from mouth, in order to avoid metal heating and appliance detachment. The purpose of the present investigation was to measure and compare temperature changes and adhesion to enamel of orthodontic appliances after different MRIs. 220 orthodontic bracket were bonded on bovine incisors and wires with different materials (stainless steel and nickel titanium) and sizes (0.014’’ and 0.019’’x0.025’’) were engaged. Appliances were submitted to MRI at two different powers (1.5T and 3T). Temperatures of brackets and wires were measured before and after MRI. Subsequently, shear bond strength (SBS) and adhesive remnant index (ARI) scores were recorded. Statistical analysis was performed. After MRI a significant increase of temperatures was found both for brackets and wires in some groups, even if the mean temperature increase was clinically not significant, as it ranged between 0.05°C and 2.4°C for brackets and between 0.42°C and 1.74°C for wires. MRI did not conditioned bracket adhesion in any group. No differences were reported when comparing 1.5T with 3T groups. ARI Scores were significantly lower after MRI. The results of the present report show that under MRI orthodontic appliances present low temperature rise and no debonding risk. Therefore, the removal of orthodontic appliance would not be recommended routinely, but could be suggested only in case of void risk or interference in image quality.